Diffusion of steroids from sol-gel glass

Samples of porous glass loaded with steroids, progesterone, estradiol, estrone, and hydrocortisone are manufactured using two different techniques. Steroids are introduced into the solution during the mixing stage of the sol-gel processing or when sol-gel samples stabilized by firing at 750 degrees C are impregnated with liquid solutions of steroids. The latter method is more advantageous, since more steroids can be introduced into the pores, and one may avoid reactions that can permanently bond steroids to the sol-gel matrix. The excess adsorption of steroids by porous sol-gel glass is explained in terms of specific interactions between the host and adsorbed materials. Analysis of infrared spectra provides information on interactions between steroids and porous sol-gel glass. Diffusion coefficients of progesterone, estradiol, estrone, and hydrocortisone are measured in pure ethanol, an ethanol-water mixture, and a physiological solution. It is shown that permeability is favored for steroids having fewer hydroxyl and carbonyl groups. Solvents that readily dissolve the drugs increase the diffusion rate. Molecular motion of steroids in small pores is more restricted than in pores of larger diameter. A possible application of porous sol-gel glass for slow drug delivery is evaluated.